On 24/02/2022 22:10, Rob Herring wrote:
On Thu, Feb 17, 2022 at 01:48:34PM +0000, Richard Fitzgerald wrote:
Some audio hardware cannot support a fixed slot width or a slot width
equal to the sample width in all cases. This is usually due either to
limitations of the audio serial port or system clocking restrictions.
This property allows setting a mapping of sample widths and the
corresponding tdm slot widths.
Signed-off-by: Richard Fitzgerald <rf@xxxxxxxxxxxxxxxxxxxxx>
---
.../devicetree/bindings/sound/audio-graph-port.yaml | 7 +++++++
1 file changed, 7 insertions(+)
diff --git a/Documentation/devicetree/bindings/sound/audio-graph-port.yaml b/Documentation/devicetree/bindings/sound/audio-graph-port.yaml
index 476dcb49ece6..420adad49382 100644
--- a/Documentation/devicetree/bindings/sound/audio-graph-port.yaml
+++ b/Documentation/devicetree/bindings/sound/audio-graph-port.yaml
@@ -71,4 +71,11 @@ patternProperties:
description: CPU to Codec rate channels.
$ref: /schemas/types.yaml#/definitions/uint32
+ dai-tdm-slot-width-map:
+ description: Mapping of sample widths to slot widths. For hardware that
+ cannot support a fixed slot width or a slot width equal to sample
A variable slot width sounds like a feature, not a limitation.
Depends on point of view. Most interfaces allow setting a fixed slot
width but in some cases that's not possible so it is more likely to be
seen as a limitation. It is however a feature in the sense that it can
avoid using higher frequencies that are necessary.
+ width. An array containing one or more pairs of values. Each pair
+ of values is a sample_width and the corresponding slot_width.
That sounds like a matrix, not an array. N entries of 2 cells each.
+ $ref: /schemas/types.yaml#/definitions/uint32-array
+
I'd think there are some constraints on the values? Slots should be at
least 8 bits, right? A max of 2x32 bits or is there more
True. I didn't think it was appropriate for a generic binding to enforce
a range when that depends on the exact hardware. But if you want I can
enforce a range that's likely to be true for all hardware.
than stereo within a slot? In any case, it's for sure no where near 2^32
max.
One sample per slot.
Is there a need for specifying where in the slot the data is?
I don't believe so, all the protocols I know of have the data bits
transmitted first followed by padding. There's no harm adding a
reserved field to allow for this info if it is ever needed, but it would
be unused at present as there's no kernel API to do this.
Rob
